Short circuit operators always evaluate in boolean context. In boolean context there are only true and false. The string "0" and numberic 0 are, among others, false. But, 0 (or empty string) is defined. So you need to check for defined-ness to allow them. See True or False? A Quick Reference Guide.

Open source softwares? Share and enjoy. Make profit from them if you can. Yet, share and enjoy!

When putting a smiley right before a closing parenthesis, do you:

Use two parentheses: (Like this: :) )
Use one parenthesis: (Like this: :)
Reverse direction of the smiley: (Like this: (: )
Use angle/square brackets instead of parentheses
Use C-style commenting to set the smiley off from the closing parenthesis
Make the smiley a dunce: (:>
I disapprove of emoticons
Other